1. Field of the Invention
The present invention relates to automated manufacturing equipment, more particularly to systems for handling electronic devices.
2. Description of the Related Art
Automated systems for electronic component assembly and test often utilize mechanical handling devices to speed processing and eliminate or reduce the potential for damage to the components. One such type of handling device is the input tube unloader 100 of FIG. 1. A tube unloader is a machine that receives plastic or metal tubes containing, for example, integrated circuits (ICs) encased in plastic leadless chip carriers (PLCCs). The contents of the tubes are generally referred to as "devices." The input tube unloader 100 is used in the beginning of a production process to rapidly and safely remove the devices from the tubes and feed them into the next machine on the production line. In this manner, devices can be automatically supplied to inspection, test, or circuit board assembly systems, to name but a few, with a minimum potential for damage in handling. FIG. 2 shows one use of the input tube unloader in a system 210 that performs visual inspection of devices. Input tube unloader 100 provides a flow of devices for inspection station 220. Devices are reloaded into tubes at output tube loader 230. The entire process is performed on a single handler support structure 240.
Input tube unloader 100 typically consists of a moving plate 310 (also sometimes referred to as a pusher plate) and a pair of side guide plates 320 to hold tube stack 330 vertically, as shown in FIG. 3. Moving plate 310 acts as a separator and guide for the tubes. Moving plate 310 moves freely atop base plate 340 using two sets of guide rods (or linear slides), bushings, bush housings and mounting blocks (not shown). The extension and retraction of moving plate 310 is controlled from below by conventional actuator means, such as a pneumatic cylinder (not shown).
The initial position of moving plate 310 is extended, so that tube stack 330 rests on top of it. At the start of operation, moving plate 310 is retracted, allowing the bottom-most tube in the stack to drop onto the unloading area of base plate 340. In a typical use, gravity is allowed to pull the devices out of the tube, through an opening 345 in guide plate 320, and onto a feedtrack 347 for conveyance to the next part of the line.
After all of the devices are released from the bottom-most tube, the moving plate is extended as shown by arrow 350 in FIG. 3 to separate the empty tube from tube stack 330. The extension of moving plate 310 also ejects the empty tube from the handler into a bin or other collection system 360 to be recycled or reused. Moving plate 310 then moves back to its retracted position, allowing tube stack 330 to drop a new bottom-most tube into position on base plate 340 for unloading. The process repeats until the machine is stopped by the operator or all tubes are emptied and ejected.
FIG. 4 shows a simplified cross-section of unloader 100. A problem with prior art tube unloaders is the rubbing between the second-to-last tube 402 and the top surface of moving plate 310, depicted in region 410 of FIG. 4, when extending to eject bottom-most tube 401. Over time, the tubes tend to wear down from this contact, losing dimensional accuracy and becoming prone to jamming. The operation is also noisy, leading to increased operator fatigue.
Additionally, because of the contact between bottom-most tube 401 and moving plate 330, the top surface of moving plate 330 can lose its coating and/or dimensional accuracy over time. This leads to jams at region 420 and the need to replace the degraded components of unloader 100.
A further drawback arises from the difference in the friction characteristics and overall design of metal tubes versus plastic tubes. Because moving plate 310 is thicker than a metal tube, tubes occasionally get stuck midway through the separation and ejection process. This type of jamming also has the potential for damaging devices in second-to-last tube 402, which is highly undesirable.
What is needed is a quiet means for separating and ejecting empty tubes that avoids damage to the tubes and the devices therein. Furthermore, an apparatus that reduces wear on both the tubes and the unloader parts is needed to reduce costs and extend equipment lifetime.